Lubricant base oils are generally prepared by fractionating a vacuum gas oil fraction into narrow boiling range fractions, and hydrocracking and/or hydroisomerizing the narrow boiling range fractions. The fractionation is generally performed prior to the hydrocracking/hydroisomerization in an effort to increase the lubricant base oil yield and to produce the highest quality lubricant base oils.
Various processes for producing lubricant base oils are known in the art. The goal of these processes is to produce lubricant base oils with high viscosity indices and low pour points.
International Publication Number WO 96/13563 teaches a process for producing a high viscosity index lubricant having a viscosity of at least 125 from a waxy hydrocarbon feed having a wax content of at least 40 weight percent (wt. %). The disclosed process comprises catalytically dewaxing waxy paraffins present in the feed primarily by isomerization, in the presence of hydrogen and in the presence of a low acidity large pore zeolite molecular sieve having a crystal size of less than 0.1 micron, an alpha value of not more than 30 and containing a noble metal hydrogenation component. The effluent of the process may be further dewaxed by either solvent or catalytic means in order to achieve target pour point.
International Publication Number WO 99/41337 teaches a method of producing a lubricant oil feedstock from a waxy feed. Waxy feeds are treated under hydroisomerization conditions to produce an isomerate product of high viscosity index by using a silica-alumina based catalyst with a pore volume of less than 0.99 ml/gm (H2O), an alumina content in the range of 35 to 55 wt. %, and an isoelectric point in the range of 4.5 to 6.5. Following isomerization the isomerate is fractionated into a lubricant cut boiling in the 330° C.+ range and a fuel cut. The lubricant fraction is then dewaxed to provide a lubricant basestock of high viscosity index.
International Publication Number WO 99/41332 teaches a method of making a wax isomerate oil having a viscosity index of from 110 to 160 and a pour point of less than −20° C. The method comprises the steps of hydrotreating a wax having a mean boiling point of from 400 to 500° C. and containing not more than 20% oil, isomerizing the hydrotreated wax over an isomerization catalyst, fractionating the resulting isomerate to recover a fraction having a viscosity in the range of about 3.0 to 5.0 cSt at 100° C. and boiling above about 340° C., and dewaxing the recovered fraction.
European Patent EP 0321307 teaches a process for the production of non-conventional lubricant oil base stocks or blending stocks of very low pour point (−21° C. or lower) and very high viscosity index (130 and higher) by the isomerization of waxes over isomerization catalysts in an isomerization unit. The total product from the isomerization unit is fractionated into a lubricant oil fraction boiling in the 330° C.+ range and a fuel cut. The lubricant oil fraction is then solvent dewaxed and unconverted wax is recycled to the isomerization unit.
International Publication Number WO 97/21788 discloses a process for the manufacture of biodegradable high performance hydrocarbon base oils. According to the process, a waxy, or paraffinic feed, particularly a Fischer-Tropsch wax, is reacted over a dual function catalyst to produce hydroisomerization and hydrocracking reactions sufficient to produce a crude fraction containing 700° F.+ isoparaffins. The methyl paraffins containing crude fraction is topped via atmospheric distillation to produce a heavy fraction having an initial boiling point between about 650 and 750° F. which is then solvent dewaxed. The dewaxed oil is then fractionated under high vacuum to produce biodegradable high performance hydrocarbon base oils.
U.S. Pat. No. 4,975,177 teaches a process of producing lubricant basestocks of high viscosity index (typically at least 130 or higher) and low pour point (typically below 5° F.) by hydroisomerizing petroleum waxes over zeolite beta and then dewaxing to target pour point. A preferred process employs a solvent dewaxing after the hydroisomerization step to effect a partial dewaxing with the separated waxes being recycled to the hydroisomerization step; dewaxing is then completed catalytically, typically over ZSM-5 or ZSM-23.
International Publication Number WO 99/41335 teaches a method for producing a lubricant basestock from a waxy feed containing 50 wt. % or more of wax. The feed is upgraded by a process comprising the steps of hydrotreating the feed to produce a material of reduced sulfur and nitrogen and hydroisomerizing the hydrotreated material over a low fluorine content, alumina based, hydroisomerization catalyst to reduce the wax content to less than about 40 wt. %. The feed is then separated into a fraction boiling below about 340° C. and a lubricant fraction boiling above about 340° C. The lubricant fraction is further processed over a catalyst comprising a mixture of a catalytically active metal component on a zeolite dewaxing catalyst and a catalytically active metal component on an amorphous catalyst. Optionally, the lubricant fraction is first solvent dewaxed before further processing.
A disadvantage of conventional processes is that they cannot effectively hydroisomerize a broad boiling range hydrocarbonaceous feedstock to produce both heavy and light lubricant base oil fractions that have acceptable pour points, viscosity indices, and yields.
When a conventional process is used to isomerize a broad boiling range feedstock to produce a high quality light lubricant base oil fraction (i.e., with an acceptable pour point and viscosity index), a relatively high pour point heavy lubricant base oil is formed. When a conventional process is used to isomerize a broad boiling range feedstock to produce a high quality heavy lubricant base oil (i.e., with an acceptable pour point and viscosity index), a relatively low viscosity index light lubricant base oil fraction is formed in relatively low yields. In order to produce both a heavy and a light lubricant base oil fraction with acceptable pour points and viscosity indices from a broad boiling range feed, the light portion is typically overdewaxed to produce heavy lubricant base oils with acceptable properties. Overdewaxing the light portion increases branching, thereby lowering the viscosity index of the light portion. The conventional solution to avoid overdewaxing a broad boiling range feedstock is to fractionate the broad boiling range feedstock into narrow boiling range fractions and then hydroisomerize each narrow boiling range fraction. This solution results in increased production cost and complexity.
It would be advantageous to provide a relatively low-cost, low-complexity process for producing a plurality of lubricant base oils with acceptable pour points, viscosity indices, and yields from a broad boiling range feedstock.